The Treaty was signed on 29 October 2004 by representatives of the then 25 member states of the European Union. It was later ratified by 18 member states, which included referendums endorsing it in Spain and Luxembourg. However the rejection of the document by French and Dutch voters in May and June 2005 brought the ratification process to an end.

Following a period of reflection, the Treaty of Lisbon was created to replace the Constitutional Treaty. This contained many of the changes that were originally placed in the Constitutional Treaty but was formulated as amendments to the existing treaties. Signed on 13 December 2007, the Lisbon Treaty entered into force on 1 December 2009.

The drafting for European Constitution began in a call for a new debate on the future of Europe at the Laeken European Council in December 2001. A European Convention was founded shortly afterward which was chaired by former French President Valéry Giscard d'Estaing and composed of two Members of Parliament (generally one from the governing majority and one from the opposition) of each Member State and applicant state, 16 MEPs, 2 members of the European Commission [1] and a representative from each government. It met in public. Giscard d'Estaing proposed to draft a Constitution. Romano Prodi, the President of the European Commission backed a draft text, called the 'Penelope Project', which contained a deeper integration of the countries and a clearer institutional model.[2]

The Treaty establishing a Constitution for Europe was signed in Rome on 29 October 2004 by 53 senior political figures from the 25 member states of the European Union. In most cases heads of state designated plenipotentiaries to sign the treaty, but some presidents also signed on behalf of states which were republics. Most designated plenipotentiaries were prime ministers and foreign ministers.

On 12 January 2005 the European Parliament voted a legally non-binding resolution in support of the Constitution by 500 votes in favour to 137 votes against, with 40 abstentions.[3]

Before an EU treaty can enter into force, it must be ratified by all member states. Ratification takes different forms in each country, depending on its traditions, constitutional arrangements and political processes. Most member states ratify EU treaties following parliamentary votes, while some — notably Ireland and Denmark — sometimes hold referendums. As a reaction to what was seen as the novel nature of the Constitution, many advocates and opponents of the Constitution argued that it should be subjected to referendums across the European Union.[4]

On 20 April 2004 then British prime minister Tony Blair unexpectedly announced an intention to hold a referendum, a proposal which he had previously rejected. A further seven member states announced or had already announced that they would hold referendums on the Constitution, these being Denmark, France, Ireland, Luxembourg, the Netherlands, Spain and Portugal.

Spain was the first country to hold a referendum on the Constitution. On 20 February 2005, Spanish voters backed the treaty with 76% voting in favour to 24% against, on a turnout of 43%.[5]

Notwithstanding the rejection in France and the Netherlands, Luxembourg held a referendum on 10 July 2005 approving the Constitution by 57% to 43%. It was the last referendum to be held on the Constitution as all of the other member states that had proposed to hold referendums cancelled them.

After the French and Dutch referendum results European leaders decided to hold a "period of reflection" on what to do next.[6] As part of this reflection period a "group of wise men" was set up to consider possible courses of action.[7] This group of high-level European politicians – former prime ministers, ministers and members of the European Commission – first met on 30 September 2006 in Rome.[8]

On 4 June 2007, this group, known as the Amato Group, presented its report. They proposed to establish a new Inter-Governmental Conference with a view to writing a new treaty which would rewrite the Maastricht Treaty, amend the Treaty of Rome and give the Charter of Fundamental Rights of the European Union a legally binding status. The new treaty would be based on the first and fourth parts of the Constitution, the rest of the Constitution's changes being achieved through amendments to the Treaty of Rome.[9]

In the June 2007 European summit meeting, Member States agreed to abandon the constitution and to amend the existing treaties, which would remain in force. They also agreed a detailed mandate for a new intergovernmental conference to negotiate a new treaty containing such amendments to the existing treaties (primarily the Treaty of Rome and the Treaty of Maastricht). These negotiations were completed by the end of the year. The new treaty, which had previously been referred to as the Reform Treaty, became the Lisbon Treaty on its signing in Lisbon on 13 December 2007.

Under the TCE, the Council of the European Union would have been formally renamed the "Council of Ministers", which is already its informal title. The "General Affairs Council" would have been formally split from the "Foreign Affairs Council", which had informally held meetings separately since June 2002.

The TCE proposed the formal recognition of a flag, an anthem and a motto for the Union, although none of them were new.

the primacy of EU law: in areas where member states have made legally binding agreements at EU level, they may not then pass national laws incompatible with those EU laws.

The TCE would have specified that the EU is a union of member states, and that all its competences (areas of responsibility) are voluntarily conferred on it by its member states according to the principle of conferral. The EU would have no competences by right, and thus any areas of policy not explicitly specified in the Constitution would have remained the domain of the sovereign member states (notwithstanding the ‘flexibility clause').

According to the TCE, the EU may act (i.e. make laws) only where its member states agree unanimously that actions by individual countries would be insufficient. This is the principle of subsidiarity, and is based on the legal and political principle that governmental decisions should be taken as close to the people as possible while still remaining effective. It is a main argument against claims that Europe limits national sovereignty but critics say that it is a principle to which lip service only is paid, and, in practice, the reach of the EU has been increasingly ambitious.

Amongst European countries, the European Court of Justice has consistently ruled since 1964 that EU law has primacy over the laws of member states in the areas where member states allow it to legislate. National law which is incompatible with an agreement already made at European level is deemed to be 'disapplied' when questions arise in courts. This controversial and fundamental principle of European Community law was first recognised in the case of Van Gend en Loos in 1963 which was followed in Costa v. ENEL in 1964.

The EU has six exclusive competences, policy areas in which member states have agreed that they should act exclusively through the EU and not legislate at a national level. The list remains unchanged from the previous treaties:

There are a number of shared competences. These are areas in which member states agree to act individually only where they have not already acted through the EU, or where the EU has ceased to act (though these are areas where member states may act both nationally and through the EU if they wish). Three new competences have been added to those in previous treaties.

There are a number of areas where the EU may take only supporting, coordinating or complementary action. In these areas, member states do not confer any competences on the Union, but they agree to act through the Union in order to support their work at national level. Again, three new competences have been added to those from previous treaties.

The TCE was going to state explicitly that the EU had a legal personality. Prior to this, the treaties explicitly stated that the European Community, the European Coal and Steel Community and Euratom each had their own separate legal personality, but remained silent over whether the European Union itself had one. They did mandate the EU "to assert its identity on the international scene,"[50] and permitted the European Union to enter into treaties. Brsakoska-Bazerkoska,[51] and Choutheete and Ndoura[52] argue that the EU had an implicit legal personality prior to the Treaty of Lisbon; the latter treaty also contained an express statement that the EU had a legal personality.

The TCE would have conferred upon the EU as new 'shared competences' the areas of territorial cohesion, energy, and space. These are areas where the EU may act alongside its individual member states. The EU has conferred upon it as new areas of 'supporting, coordinating or complementary action' the areas of tourism, sport, and administrative co-operation.

Member states would have continued to co-operate in some areas of criminal judicial proceedings where they agree to do so, as at present. Under the TCE, seven new areas of co-operation would have been added:

The new solidarity clause of the TCE specifies that any member state which falls victim to a terrorist attack or other disaster will receive assistance from other member states, if it requests it. The type of assistance to be offered is not specified. Instead, the arrangements will be decided by the Council of Ministers should the situation arise.[53]

The TCE includes a copy of the Charter already agreed to by all EU member states. This is included in the Constitution so that EU institutions themselves are obliged to conform to the same standards of fundamental rights. At the time of the Charter's original agreement, the British Government said that it did not have binding effect. Incorporation into TCE would have put its importance beyond doubt.

The TCE made an effort to simplify jargon and reduce the number of EU legal instruments. However, it is a long document couched in obscure and technical terms, which proved unpopular when presented (for example) to French voters in their referendum on the TCE.

More day-to-day decisions in the Council of Ministers would be to be taken by qualified majority voting, requiring a 55% majority of members of the Council representing a 65% majority of citizens. (The 55% is raised to 72% when the Council acts on its own initiative rather than on a legislative proposal from the Commission or the Union Minister for Foreign Affairs.) The unanimous agreement of all member states would only be required for decisions on more sensitive issues, such as tax, social security, foreign policy and defense.

The six-month rotating Presidency of the European Council would switch to a chair chosen by the heads of government, in office for 2½ years and renewable once. The role itself would remain administrative and non-executive, but rather than the Presidency being held by a member state as at present, it would be held by an individual elected by and accountable to the Council.

The six-month rotating Presidency of the Council of Ministers, which currently coincides with the Presidency of the European Council, would be changed to an 18-month rotating Presidency shared by a trio of member countries, in an attempt to provide more continuity. The exception would be the Council's Foreign Affairs configuration, which would be chaired by the newly created Union Minister for Foreign Affairs.

Parliament as co-legislature: The European Parliament would acquire equal legislative power under the codecision procedure with the Council in virtually all areas of policy. Previously, it had this power in most cases but not all.

Budget: The final say over the EU's annual budget would be given to the European Parliament. Agricultural spending would no longer be ring-fenced, and would be brought under the Parliament's control.

Role of national parliaments: Member states' national parliaments would be given a new role in scrutinising proposed EU laws, and would be entitled to object if they feel a proposal oversteps the boundary of the Union's agreed areas of responsibility. If the Commission wishes to ignore such an objection, it would be forced to submit an explanation to the parliament concerned and to the Council of Ministers.

Popular initiative: The Commission would be invited to consider any proposal "on matters where citizens consider that a legal act of the Union is required for the purpose of implementing the Constitution" which has the support of one million citizens. The mechanism by which this would be put into practice has yet to be agreed. (See Article I-46(4) for details.)

There would have been a tightening of existing rules for 'enhanced cooperation', where some member states would have chosen to act together more closely and others not. A minimum of one third of member states would now be forced to participate in any enhanced cooperation, and the agreement of the European Parliament is needed. The option for enhanced cooperation would also be widened to all areas of agreed EU policy.

Traditionally amendments to the EU treaties were considered in inter-governmental conferences in which the European Council would meet in long private sessions in order to reach unanimous agreement on the proposed changes. The Convention which wrote the draft constitutional treaty was quite different in this regard. It met in public and was composed of a mix of national and European politicians. The Constitution proposed that amendments to the Constitution would be drafted by a convention unless both the Council of Minister and the European Parliament agreed otherwise.

A simplified revision was created for changes which might be proposed to be made to Title III of Part III of the TCE on the internal policies and action of the Union. Changes to this Title could be made by a decision of the European Council subject to it being ratified by all member states.

A new clause in the TCE provided for the unilateral withdrawal of any member state from the Union (clause I-60). Under this clause, when a country notifies the Council of its intent to withdraw, a settlement is agreed in the Council with the consent of Parliament. If negotiations are not agreed within two years, the country leaves anyway. An identical provision was subsequently inserted into the treaties by the Lisbon Treaty.

^Article IV-447 of the Treaty requires that instruments of ratification be deposited with the Government of the Italian Republic in order for the Treaty to enter into force. Each country deposits the instrument of ratification after its internal ratification process is finalised by all required state bodies (parliament and the head of state). Countries are ordered according to the date of deposition of ratification documents. When two countries have deposited the necessary documents on the same date the order is alphabetical.

^Results refer to the final round of parliamentary vote when more than one vote is required.

^Åland is an autonomous province of Finland. It is part of the European Union, but is subject to certain exemptions. Åland is not party to the Treaty to establish European constitution, but according to Article IV-440, Paragraph 5 the Treaty will apply on the territory but with derogation. So Åland Parliament ratification is not necessary for the European Constitution to enter into force, but it is needed for provisions of Article IV-440, Paragraph 5 to be applied.